This invention relates to a method for reviewing a defect occurring in a semiconductor production process and an apparatus for the method. More particularly, the invention relates to a method for reviewing a defect, and an apparatus for the method, that will be suitable for reviewing in detail a defect by using an electron microscope.
Foreign matters, if any, on a semiconductor substrate (wafer) may result in defects such as inferior insulation and short-circuit of wiring in a semiconductor production process. With miniaturization of semiconductor chips, finer foreign matters may result in insulation defects of capacitors and breakdown of a gate oxide film. These foreign matters are generated for various causes such as those which occur from movable portions of a conveyor apparatus, those occurring from the human body, those formed as reaction products of a process gas inside a processing apparatus, those mixing in chemicals and materials, and they mix in various forms under various states. Examples are scratches on the semiconductor wafer, residues of the materials, particles, and so forth, and all of them affect production through-put.
It is therefore necessary to detect the defects occurring on the semiconductor substrate during the production process, to classify the defects detected and to identify in an early stage the occurrence source of the defects, and to prevent the mass occurrence of defects.
As a method of clarifying the causes of such defects, a method has been employed in the past that involves the steps of applying dark visual field illumination to the surface of the semiconductor substrate by using an optical foreign matter inspection apparatus to detect scattered light from the foreign matters and to stipulate the positions of defects, or detecting a bright visual field optical image of the semiconductor substrate by using an optical appearance inspection apparatus, comparing this optical image with a reference image to stipulate the positions of the defects on the semiconductor substrate, reviewing in detail the defects the position of which are stipulated through an SEM (Scanning Electron Microscope), classifying the defects, comparing them with a database and estimating the occurrence causes of the defects. Such a reviewing method is disclosed in JP-A-2001-133417, JP-A-2003-007243 and JP-A-05-041194.
To improve through-put of inspection when the foreign matters on the surface of the semiconductor substrate are detected by using the optical foreign matter inspection apparatus, the spot size of a laser beam for the dark visual field illumination of the semiconductor substrate surface is increased and the surface of the semiconductor substrate is scanned. Therefore, accuracy of the position coordinates determined from the position of the laser beam spot that scans the semiconductor substrate surface contains a large error component.
When the defect is reviewed in detail by using the SEM on the basis of the position information of the defect containing such a large error component, the defect to be reviewed is not contained in some cases in the image of the SEM that reviews the image in an incomparably higher magnification ratio than the optical foreign matter inspection apparatus. To bring the image of the defect to be reviewed into the visual field of the SEM in such a case, the defect is searched out while being moved inside the visual field of the SEM, but this is time consuming and results in the drop of through-put of the SEM observation.
The optical appearance inspection apparatus executes bright visual field illumination of the semiconductor substrate as the reviewing object and compares the image taken with a reference image to detect the defect. When the surface of the semiconductor substrate is covered with an optically transparent film, however, a defect existing inside or below the optically transparent film is detected, too, besides the defect existing on the surface of this film.
When the defect is reviewed in detail by the SEM on the basis of the position information of the defect detected by the optical appearance inspection apparatus, the defect detected by the optical appearance inspection apparatus and existing inside or below the film cannot be detected by the SEM because the SEM can generally acquire only the information of the sample surface. In such a case, the inspection apparatus using the SEM is likely to conclude that the optical appearance inspection apparatus makes wrong detection.